Electromagnet driving circuit



June 22, 1965 I A. RESZKA 3,191,101

ELECTROMAGNET DRIVING CIRCUIT Filed June 6, 1962 FIG. I j ag i 0 ta th to 5m:

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v. COLLECTOR -1 I c E x I oou pm m UPPERMOST PUNCH P|N....C POSITION MOTION 3 Zip- //-PAPER TAPE INVENTOR ALFONS RESZKA TIME MILLSECONDS United States Patent 3,191,101 ELECTRQMAGNET DRIVING CIRCUIT Alfons ltieszlra, Chicago, 'Ill., assignor to Teletype Corporation, Slrohie, 111., a corporation of Delaware June 6, 1962, Ser. No. 200,431 14 Claims. (Cl. 317-451) This invention relates to driving circuits for electromagnets and more particularly to a driving circuit for operating the electromagnet of high speed perforating or recording apparatus utilized in telegraph and like systems.

In the field of data communications, it is frequently desirable to utilize control tapes to receive and store information usually in the form of perforations representing permutation codes. Such tapes are used to supply information to or to receive information from data communication apparatus such as telegraph systems or computers. In the transfer of information between computers or on a high speed telegraph line it is especially desirable to store the information on the tape at high speeds so that the telegraph line or computer may be freed rapidly thus readying it for further use.

In the past, the perforating apparatus which was used to transfer the information from the telegraph receiver or computer to a control tape was limited in the speed at which it could be operated by inherent mechanical features of the apparatus. The mechanical limitations of such conventional tape perforators have been overcome by the intelligence recording apparatus disclosed in the copending application of W. I. Zenner, No. 811,714 filed May 7, 1959, now Patent No. 3,056,546, issued October 2, 1962. That application discloses a tape perforator which utilizes the natural frequency of vibrating reeds or metal bars to drive the punch pins of the perforator. An electromagnet is associated with each reed and is normally energized to hold its respective reed in a flexed position. The magnet is deenergized in response to input pulses to cause its associated reed to be released from its flexed position to drive the punch; and the magnet is reenergized by the time the reed returns to its original flexed position to hold the reed until receipt of the next input pulse.

In order to drive the electromagnets of the tuned reed perforators disclosed in the above-mentioned application it was found that conventional electromagnet driving circuits were inadequate. Since the speed of operation of such a punch is intended to be anywhere from zero to 2,000 or 3,000 words per minute, the energizing circuits must be capable of extremely rapid operation. When conventional turn-on, turn-off circuits are used to achieve these speeds, it is necessary that the ratio of the coil inductance to the discharge resistance be small. In order to achieve this small ratio, the discharge resistance must be large which results in excessive power loss in the resistor. Furthermore, in these conventional turn-on, turn-off circuits it has been found that the voltage surges due to the collapse of the field in the coil when the current is interrupted are diflicult to dissipate at the high speeds at which the perforator is operated.

Therefore, it is an object of this invention to provide a driving circuit for an electromagnet capable of high speed operation.

It is another object of this invention to eliminate voltage surges from the driving circuit for an electromagnet when the magnet coil current is interrupted.

It is a further object of this invention to eliminate excessive power dissipation from. a driving circuit for an electromagnet.

It is still another object of this invention to utilize .a

ice

resonant circuit, of which the magnet coil is a part, in a driving circuit for an electromagnet.

It is a more specific object of this invention to provide a first resonant circuit for charging an energy storage device and to provide a second resonant circuit including the coil of an electromagnet and the energy storage device whereby the energy stored in the storage device is discharged into the electromagnet coil to elfect operation of the electromagnet.

In accordance with a preferred embodiment of this invention .a separate driver circuit is provided for each one of a plurality of vibratory reeds which furnish energy for actuating punches in accordance with the disclosure of the copending application No. 811,714 mentioned hereinbefore. The coil of each of the electromagnets associated with the reeds is normally energized causing the electromagnet to attract its associated reed from a neutral position to a stressed position. A normally nonconductive silicon controlled rectifier is connected in series with a first resonant circuit comprising an inductance and a capacitor. When an input pulse is applied to the gate electrode of the rectifier, it is rendered conductive and causes the capacitor to be charged from a source of D.C. supply. This first resonant circuit is prevented from oscillating by the silicon controlled rectifier and a diode thereby causing the charge to remain on the capacitor. The capacitor is also connected through a normally nonconducting transistor to the coil of the electromagnet. Immediately following the charging of the capacitor through the first resonant circuit, the transistor is rendered conductive thereby allowing the capacitor to discharge through the electromagnet coil. This discharge current is in opposition to a holding current normally flowing through the coil and. is of sufficient magnitude to overcome or swamp out the holding current. The coil and the capacitor form a second resonant circuit, and the frequency of this circuit is chosen in accordance with the natural frequency of the reed, so that the complete discharge of the capacitor takes place by the time the reed reaches its lowest point of travel in the punching cycle. The holding current through the coil then is reestablished in time to attract and hold the reed upon its return halfcycle of vibration.

Further objects and features of the invention will be come apparent to those skilled in the art upon con sideration of the following detailed specification taken in conjunction with the drawings in which;

FIG. 1 is a circuit diagram of a preferred embodiment of the invention, and 1 FIG. 2 shows wave forms helpful in understanding the operation of the circuit of FIG. 1.

Referring now to the drawing, FIG. 1 shows an electromagnet for a vibrating reed punch having a laminated core 10 with three legs 11, 12 and 13. A normally energized driver coil 14 is wound about the center leg 12 of the core 11) to attract one end of a reed or bar 15 which comprises the armature for the electromagnet. By suitably fixing the other end of the reed 15 to a supporting block 16, the reed 15 is held in a stressed position when the coil 14 is energized. The inner end of the reed 15 is connected by a link 17 to a punch pin 18. When the reed 15 is released by deenergization of the coil 14, the punch pin 18 passes through a guide aperture 19 in a punch block 29 to effect punching of the tapepassing between the punch block 20 and a suitable aperture in a die plate 20A.

The driver coil 14 of the electromagnet is energized in its quiescent condition by current passing from. ground to a negative battery 21. The amount of this current is regulated by a variable resistor 22 connected in series with the parallel combination of a thermistor 23 and a resistor 24- which compensate the circuit for variations of temperature. An inductor 25 is connected between the coil 14 and the parallel combination of the thermistor 23 and the resistor 24 for reasons which will be explained hereinafter.

When it is desired to operate the punch, the coil 14 is deenergized by applying a current in opposition to the holding current supplied by negative battery 21. This causes the electromagnet to release the reed 15 which then tends to return to its neutral position. As the reed 15 is released by the electromagnet, the reeds potential energy is converted to kinetic energy and its associated punch 18 strikes the tape at a point just beyond the reeds neutral position where part of the energy is dissipated in effecting the punching operation. However, the reed 15 retains sufficient kinetic energy to continue its move inent beyond its neutral position; and in a succeeding portion of the cycle of its vibration, the reed moves back toward the core of the electromagnet. By this time, the deenergizing pulse of current through the coil is terrninated, thereby allowing the holding current from the negative battery 21 to be reestablished in the coil 14 causing the electromagnet to attract and hold the reed 15. The reed 15 is held in a stressed position until the magnet is again deenergized. This basic operation of the vibrating reed perforator is more fully described in the copending application No. 811,714 referred to above, and the specification of that application is incorporated herein by reference.

In order to effect the deenergization of the driver coil 14 as stated above, input pulses from a suitable source (not shown) are applied through a terminal 26, a coupling capacitor 27 and a diode 2% to the gate electrode of a silicon controlled rectifier 2 to trigger the silicon controlled rectifier 29 into conduction. The silicon controlled rectifier 29 and a diode 30 are connected in series between an inductance 31 and a capacitance 32 which form a first resonant circuit. Operating potential for this circuit is supplied from a source of positive battery 33.

When the circuit is in its quiescent condition, the silicon controlled rectifier 2% is nonconducting and the capacitor 32 is fully discharged thereby causing the cathode I of the silicon controlled rectifier 29 to be at or near ground potential since the capacitor 32 is grounded. When an input triggering pulse is applied to the gate electrode of the silicon controlled rectifier 29 to initiate conduction, the rectifier 29 conducts and a holding current is maintained therethrough which causes the capacitor 32 to start charging resonantly through the inductor 31. The voltage drop across the diode 39 during the charging of the capacitor 32 is applied across the emitter-base electrodes of a PNP transistor 34 and maintains that transistor in a nonconductive state, since the potential applied to the base of the transistor is positive with respect to the potenial applied to the emitter as a'result oi the voltage drop across the diode 30.

A parallel combination of a resistor '35 and a Zener diode 36 is connected across the emitter and collector electrodes of the transistor 34. The resistance of the resistor 35 is chosen to be high, so that with the transistor 34 biased to its nonconductive state, the resistance 35 presents a high impedance to the charging circuit for the capacitor 32. As a consequence the resonant circuit including the inductor 31 and the capacitor 32 tends to oscillate. However, at the end of the first half-cycle, when the current tends to reverse, the silicon controlled rectifier 29 reverts to a blocking state and with the diode 30 opposes any reverse current flow thereby leaving the capacitor 32 charged to a voltage greater than that supplied by the positive battery 33. As soon as the charging current ceases to flow through the diode 30, the transistor 34 is switched into full conduction since the potential at its emitter is now positive with respect to the bias potential applied to its base by means of a voltage divider consisting of a diode 38 and a pair of resistors 39 and 49 connected in series between a positive battery 37 and ground.

When transistor 34 is rendered conductive, the capacitor 32 discharges resonantly through the transistor 34 into the coil14 and swamps out or overcomes the holding current in the coil 14 since the discharge current is in opposition to the holding current. The field in the coil collapses and the reed 15 is released to punch the paper tape. The Zener diode 36 limits the voltage across the transistor E34. to a safe value. v

The resistance of resistor 35 must be suificiently high to insure that the resonant circuit comprising the inductor 31 and the capacitor 32 tends to oscillate. If the resistance of the resistor 35 were too low, a relatively large amount of current from the battery 33 would flow through it to the coil 14 and the aforementioned circuit would not tend to oscillate and would not cause a reverse flow of current. As a consequence, the silicon controlled rectifier would not revert to a biocking state, but would continue conduc ing indefinitely.

The inductance of the inductor 25 is chosen with respect to the inductance of the driver coil 14 so that the inductor 25 presents a high A.C. impedance compared to that of the coil 14. The ratio of the AC. impedance of the inductor 25 to that of the coil 14 is chosen to be of the order of ten to one. This is necessary in order to prevent the discharge of the capacitor 32 from taking place through the resistors 22, 23 and 24 to the negative battery Zi instead of through the driver coil 14. It is readily apparent that the inductor 25 will have little or no effect upon the DC. holding current normally passing through the driver coil 14.

The frequency of the second resonant circuit, comprising the capacitor 32 and the driver coil 14, is chosen to be such that the capacitor 32 is fully discharged at about the time the reed 15 is at its lowest point of travel. At that time, the holding current is restored in the coil 14 since it is no longer opposed by current from the capacitor 32, and the electromagnet pulls the reed 15 back to its uppermost position where it is held until another energizing pulse is received at terminal 26. When the capacitor 32 is fully discharged, the potential on the emitter of the transistor 34 is at or near ground level, and the potential applied to the base of the transistor 34 from the voltage divider 38, 39, and 40 is positive with respect to that applied to its emitter by the capacitor 32 thereby causing the transistor 34 to be rendered nonconductive.

Since the circuit including the coil 14 and the capacitor 32 tends to be oscillatory, current in the coil 14 then tends to cause an inverse charge to appear across the capacitor 32; but a diode 41 is connected across the capacitor 32 and shunts the inverse current through the resistor 35 and the Zener diode 36 which cause oscillations to be quickly damped. As a result, the quiescent condition of the system is reached before the next punching cycle begins. In addition to shunting the current discharge, the diode 41 clamps the capacitor 32 to ground thereby insuring that the silicon controlled rectifier 29 is not refired by a negative voltage developed in the capacitor 32 by the discharge current.

The diode 28 protects the gate of the silicon controlled rectifier 29 from the high reverse voltage present when the capacitor 32 is fully charged. In addition, the system is rendered relatively insensitive to triggering by spurious noise pulses by connecting the anode of'the diode 23 to a. voltage divider comprising resistors 42 and 43 which are connected between the grounded terminal of the capacitor 32 and a negative battery 44. This voltage divider maintains on the anode of the rectifier 28 a negative voltage which is overcome by the signal input pulses but which exceeds the magnitude of positive noise pulses which might otherwise trigger the silicon controlled rectifier 29 into conduction. The diode 28 also prevents any input pulses from firing the silicon controlled rectifier 29 until the capacitor 32 is fully discharged.

A resistor 45'is connected between the negative battery 44 and the junction of the cathode of the diode 28 with the gate electrode of the silicon controlled rectifier 29. This resistor 4-5 acts as a stabilizing resistor in the circuit and references the gate electrode of thesilicon controlled rectifier 29 to ground which results in a more reliable turn off of the silicon controlled rectifier 29.

The operation of the circuit shown in FIG. 1 may be more fully understood when taken in conjunction with the wave forms shown in FIG. 2. As stated previously, when the system is in its quiescent condition, the capacitor 32 is discharged and transistor 34 is biased oil? by means of the voltage divider comprising diode 38 and resistors 39 and 40 connected to its base. The punching cycle is initiated when a positive pulse, such as that shown in curve A of FIG. 2, is applied to the terminal 26. This pulse triggers the silicon controlled rectifier 29 into conduction and causes the capacitor 32 to charge resonantly through the inductor 31 from time 0 to ta. The potential on the emitter of the transistor 34 is the same as the potential being stored in the capacitor 32, and this potential with respect to time is shown in curve B of FIG. 2.

As long as current flows through the diode 30, the potential on the emitter of the transistor 34 is negative with respect to that applied to its base and the transistor remains nonconducive. This is shown in curve D of FIG. 2 which represents the voltage on the collector of the transistor 34 with respect to the emitter. It is seen that during the initial time interval 0 to ta this voltage becomes increasingly negative.

During this initial time interval 0 to ta a portion of the current flow through the silicon controlled rectifier 29 also flows through the resistor 35 to the'driver coil 14. As a result, the potential on the collector of the transistor 34 rises slightly while the capacitor 32 is being charged. Wave form C, which represents the potential on the collector of the transistor 34 with respect to time, shows this rise in the collector potential of the transistor 34 during the time interval 0 to ta.

This current flowing through the driver coil 14- begins the deenergization of the coil prior to the discharge of the capacitor 32. Wave form E, which represents the current flow through the coil 14 with respect to time, shows the rise in current flow during the time interval 0 to ta from the normal quiescent negative value toward zero current.

t time in, the resonant charging circuit comprising the coil 3T and the capacitor 32 tends to oscillate; but as stated previously, this oscillation is blocked by the action of the silicon controlled rectifier 29 and diode 30. At the same time, time la, the transistor 34 is rendered conductive and remains conductive until time tb at which time the capacitor 32 is fully discharged and the transistor 34 is rendered nonconductive by the bias potential applied to its base from the source 37. During the interval between times ta and tb the capacitor discharges through the transistor 34 and swamps out the holding current in the coil as seen by reference to wave form E of FIG. 2. The voltage on the capacitor 32 and on the emitter of transistor 34 is at ground at time th and the transistor is cut oil as may be seen by reference to wave form B and C.

At the time ta, the reed is released by the electromagnet since the driver coil 14 no longer has sufiicient holding current flowing through it; and the punch pin 18 is driven toward the paper tape as seen in curve F which represents the physical movement of the punch pin with respect to time. The punch pin 18 is at or near its lowest position at time tb and the reed begins to return upward. At this same time, the holding current shown in curve B again becomes sulficient to attract the reed 15 so that when the reed completes its cycle and returns to its uppermost position, at time to, it is held there by the negative holding current through the coil :14.

It will be noted that during the time interval between times tb and to, the voltage on the collector of transistor 34 becomes somewhat negative with respect to that of its emitter. This is caused "by the oscillatory tendencies of the resonant circuit including the capacitor 32 and the coil 14.

The tendency for the circuit to oscillate is further apparent from examination of the wave form E between the times tb and to. It is noted that the current flowing through the coil drops to a value slightly below the normal holding current which was flowing through it. at time 0. The damping effect due to resistor 35 and Zener diode 36 then prevents any further oscillation from occurring. The rise of current in the coil to the value X shown in wave form E is caused by the fact that as the reed 15 approaches the coil 14, it causes a current to be generated in the coil 14 in opposition to the normal holding current. However, the negative holding current is sufiicient to attract and hold the reed 15 so that at the time to, the system is once again in its quiescent condition and is ready for receipt of another input signal on terminal 26 at which time the foregoing cycle of operation will be repeated.

By utilizing a resonant circuit to effect deenergization of the driver coil 14, undesirable voltage surges have been eliminated when the coil current is interrupted since the natural resonant phenomena of the circuit are followed. The resonant circuit of this invention also lends itself easily to operation at high speeds since the frequency of operation is a function of the inductance of the coil 14 and the energy storage capacitor 32 which form the resonant circuit.

It is necessary that the resonant frequency of the circuit comprising the capacitor 32 and the coil 14 be chosen in accordance with the natural frequency of vibration of the reed 15 with which the circuit must operate. This relationship has 'been discussed above in conjunction with wave forms E and F of FIG. 2. The resonant frequency is determined by the capacitance of capacitor 32 and the inductance of coil 14. The proper amount of holding current to maintain the reed in its stressed quiescent condition is adjusted by the setting of the variable resistor 22. Of course, the magnitude of the positive battery 33 must be sufiicient :to allow the capacitor 32 to store enough energy to overcome the holding current in the coil 14 when the energy is released.

There is no critical relationship which must be maintained between the frequency of the resonant charging circuit comprising the inductor 31 and the capacitor 32 and the frequency of the resonant deenergizing circuit comprising the coil 14 and the capacitor 32 other than the relationships discussed in the previous paragraph. It is desirable to charge the capacitor 32 as rapidly as is pnactical under the conditions of operation. As a result, the resonant frequency of the charging circuit is generally much higher than that of the deenergizing circuit as may be seen in FIG. 2 where the time interval from 0 to la represents /2 cycle of oscillation of the charging circuit and the time from ta to tb represents approximately /2 cycle of oscillation of the deenergizing circuit.

This invention has been discussed in detail with reference to a specific preferred embodiment but it will be apparent to those skilled in the art that modifications and changes may be made without departing from the spirit from oscillating and for causing said stored energy to be released in said second resonant circuit.

2. An electrical circuit including (a) an energy storage means for storing electrical '(b) first and second resonant circuits each including said energy storage means as a common element thereof,

(c) means for supplying energy from a source to said first resonant circuit, said energy being stored in said storage means, and

(d) means for preventing sai-d first resonant circuit from oscillating and for causing said stored energy to be released in said second resonant circuit.

3. In a circuit for supplying energy to an inductor,

(a) means for storing electrical energy,

(b) a first resonant circuit,

() a second resonant circuit including said inductor,

((1) said first and second resonant circuits each including said energy storing means as a common element thereof, I

(e) means for supplying electrical energy from a source to said first resonant circuit to store energy in said storing means, and

(f) means for preventing said first resonant circuit from oscillating and for causing said stored energy to be released to said inductor in said second resonant circuit.

4. In a circuit for supplying energy to an inductor,

(a) a storage capacitor,

(b) first and second resonant circuits, said second resonant circuit including said inductor and both of said resonant circuits including said capacitor as a common element thereof,

(0) means for supplying electrical energy from a source to said first resonant circuit to store energy in said capacitor, and

(d) means for preventing said first resonant circuit from oscillating and for causing said stored energy to be released to said inductor in said second resonant circuit. 7

5. A system for supplying energy to an inductor including (a) a storage capacitor,

(b) first and second resonant circuits, said second resonant circuit including said inductor and both of said resonant circuits including said capacitor as a common element thereof, a

(0) means for supplying electrical energy from a source to said first resonant circuit whereby said first resonant circuit tends to be shocked into oscillation to store energy in said capacitor, and

(d) means for preventing said first resonant circuit from oscillating and for causing said stored energy 7 (a) means for normally energizing said inductor from I a first source of direct current energy,

(b) a storage capacitor, 7

(c) first and second resonant circuits, said second resonant circuit including said inductor and both of said resonant circuits including said capacitor as a common element thereof,

(d) means for supplying direct current energy from a second source to said first resonant circuit whereby said first resonant circuit tends to be shocked into oscillation to store energy in said capacitor,

(e) blocking means for preventing said first resonant circuit from oscillating, and t (f) means responsive to said blocking means for causing said stored energy to be released to said inductor in said second resonant circuit, said released energy t? being in opposition to the energy supplied to said inductor from the first source.

7. A system for deenergizing a normally energized inductor including o (a) means forrnormally energizing said inductor from a first source of direct current energy, (b) a storage capacitor,

(0) first and second resonant circuits, said second resonant circuit including said inductor and both of said resonant circuits including said capacitor as a common element thereof,

(d) switching means connected in series with said first resonant circuit and a second source of direct current energy for supplying direct current energy from the second source to said first resonant circuit in response to input signals to cause said first resonant circuit to be shocked into oscillation thereby to store said energy in said capacitor,

(e) blocking means for preventing said first resonant circuit from oscillating, and

(f) means responsive to said blocking means for causing said stored energy to be released to said inductor in said second resonant circuit, said released energy being in opposition to the energy supplied to said inductor from the first source and being sufiicient to deenergize said inductor.

8. In a system for deenergizing a normally energized inductor,

(a) means for normally energizing said inductor from a first source of direct current energ' (b) a storage capacitor,

(0) first and second resonant circuits, said second resonant circuit including said inductor and both of said resonant circuits including said capacitor as a common element thereof,

((1) electronic switching means connected in series with said first resonant circuit and a second source of direct current energy for allowing current to flow from the second source to said first resonant circuit in response to input pulses applied to said switching means to cause said capacitor to store the energy supplied from the second source and causing said first resonant circuit to tend to oscillate,

(e) blocking means for preventing said first resonant circuit from oscillating, and

(f) means responsive to said blocking means for causing said stored energy to be released to said inductor in said second resonant circuit in opposition to the energy supplied to said inductor from the first source, said released energy being suflicient to deenergize said inductor.

In a system for deenergizing a normally energized inductor, I

(a) a first source of direct current energy for normally energizing said inductor,

(b) a storage capacitor,

(c) first and second resonant circuits, said second resonant circuit including said inductor and both of said resonant circuits including said capacitor as a common element,

((1) first electronic switching means connected in series with said first resonant circuit and a second source of direct current energy for allowing current to fiow from the second source to said first resonant circuit in response to input pulses applied to said switching means thereby to cause said capacitor to store the energy supplied from the second source and to cause said first resonant circuit to V tend to oscillate,

(e) said first electronic switching means preventing said first resonant circuit from oscillating when said capacitor is charged thereby terminating current flow in said first resonant circuit, and

(f) second electronic switching means responsive to said termination of current flow to cause said capacitor to discharge into said inductor in opposition to the energy supplied to said inductor from said first source, said discharged energy being sufiicient to deenergize said inductor.

10. A system for deenergizing a normally energized electromagnet coil including (a) a first source of direct current for normally energizing said coil,

(b) an inductor,

(c) a capacitor,

(d) said inductor and said capacitor connected to form a first resonant circuit,

(e) said coil and said capacitor connected to form a second resonant circuit,

(f) first electronic switching means connected in series with said first resonant circuit and a second source of direct current energy for allowing cur-rent to flow from the second source to said first resonant circuit in response to input pulses applied to said first switching means to cause said capacitor to store energy supplied from the second source,

(g) unidirectional conducting means connected in series with said first resonant circuit and said first switching means,

(h) second electronic switching means connected in series with said coil and said capacitor in said second resonant circuit, said second switching means being rendered nonconductive when charging current flows through said unidirectional conducting means to said capacitor,

(i) said first switching means and said unidirectional conducting means preventing said first resonant circuit from oscillating when said capacitor is charged thereby terminating current flow in said first resonant circuit,

(j) said second switching means being rendered conductive when said current flow in said first resonant circuit is terminated whereby said capacitor discharges said stored energy into said coil in opposition to said energizing current, said discharged energy being suflicient to deenergize said coil, and

(k) means effective to render said second switching means nonconductive when said capacitor completes its discharge.

11. A system according to claim wherein said first switching means is a silicon controlled rectifier.

12. A system according to claim 10 wherein said second switching means is a transistor.

13. A system for deenergizing a normally energized electromagnet coil including (a) a source of energizing current for said coil for normally energizing said coil,

(b) an inductor and a capacitor connected to form a first resonant circuit,

(0) means connecting said coil and said capacitor to form a second resonant circuit,

(d) a silicon controlled rectifier and a first diode connected in series between said capacitor and said inductor,

(c) said silicon controlled rectifier being rendered conductive in response to input pulses to allow current to flow from a second direct current source through said first resonant circuit to charge said capacitor,

(f) a transistor having at least base-emitter and emitter-collector conducting paths,

(g) said first diode being connected in parallel with said base-emitter path and said emitter-collector path being connected between said capacitor and said coil,

(h) a damping impedance connected in parallel with said emitter-collector path, and

(i) a shunt diode connected across said capacitor,

(j) said first diode and said shunt diode being poled in opposition to one another.

14. A system according to claim 13 wherein said first diode and said silicon controlled rectifier prevent said first resonant circuit from oscillating and said first diode renders said transistor nonconducting when charging current is flowing to said capacitor, said transistor being rendered conducting when said charging current ceases to flow, and additional means for rendering said transistor nonconducting when said capacitor has discharged into said coil.

References (Iited by the Examiner UNITED STATES PATENTS 2,907,929 10/59 Lawson 317-151 X 2,925,585 2/60 Bruce. 3,049,650 8/62 Greenblatt 317----148.5 3,056,906 10/62 Peters.

OTHER REFERENCES Applications and Circuit Design Notes of the Silicon Controlled Rectifier, General Electric Company, December 1958, pages 54-58.

Stahl et al.: Core Driver, IBM Technical Disclosure Bulletin, volume 2, No. 1, June 1959, page 26.

SAMUEL BERNSTEIN, Primary Examiner. 

1. AN ELECTRICAL SYSTEM INCLUDING (A) AN ENERGY STORAGE MEANS FOR STORING ELECTRICAL ENERGY, (B) FIRST AND SECOND RESONANT CIRCUITS EACH INCLUDING SAID ENERGY STORAGE MEANS AS A COMMON ELEMENT THEREOF, (C) MEANS FOR SUPPLYING ELECTRICAL ENERGY TO SAID FIRST RESONANT CIRCUT, SAID ELECTRICAL ENERGY BEING STORED IN SAID STORAGE MEANS, AND, (D) MEANS FOR PREVENTING SAID FIRST RESONANT CIRCUIT FROM OSCILLATING AND FOR CAUSING SAID STORED ENERGY TO BE RELEASED IN SAID SECOND RESONANT CIRCUIT. 